The present invention relates generally to flex circuits and rigid flex circuits, and more particularly to the embedding of devices into flex circuits and rigid flex circuits.
Flex and rigid flex circuits are used extensively in applications, including automotive, computers and peripherals, small consumer devices, medical electronics, telecommunications, military, and aerospace, where space utilization and weight are a premium.
Flex circuitry incorporates metal lines sandwiched between non-conductive flexible layers to save space in routing of metal interconnect lines. However, as more layers of metal and non-conductive substrates are added to the sandwich, the flex circuit becomes less flexible. Attempts to add electrical or electronic devices require the mounting of components onto the surfaces of a flex sandwich. The surface mounted components, i.e., surface mounted devices (SMDs), make the flex circuit even more rigid and less flexible.
Electronic systems are often separated onto two or three circuit boards. Rigid printed circuit boards (PCBs) are used to mount and support the electronic devices and include many copper layers to interconnect the respective SMDs. Separate flexible interconnects are used to provide interconnection between the rigid PCBs. Flexible circuits are typically structured with two or more metal layers. Thus, the system is somewhat flexible in the interconnect flex circuit regions, but rigid where components are mounted. Therefore, the multi-component system is not optimized for size and weight parameters.
Furthermore, the combined PCB-flex manufacturing processes are complex. Rigid flex technology employs methods to thicken and stiffen a region of the flexible circuit to provide a region that is mechanically rigid to accommodate fragile components, e.g., surface mount devices and through hole connectors.
The process for inclusion of SMDs is likewise complex and less cost effective. For example, over-molding of devices such as semiconductor circuits, require additional assembly and packaging process steps. A component device, e.g., a light emitting diode (LED), likewise is diced from a wafer, assembled into a packaged device, and the packaged device is then mounted to a PCB to complete assembly.
In addition, the aforementioned PCB substrates are poor conductors of heat. Therefore, when heat generated by the mounted device is excessive, e.g., in the case of LEDs, power circuits, microprocessors, etc., more expensive thermally conductive substrates accompanied with the attachment of a bulky conducting heat sink are required. The heat sink is attached to the underside of metal core substrate, PCB, or on top of the packaged SMD to transfer the heat away from the mounted device. The heat sink is typically metallic copper or aluminum and its attachment to the substrate or package make the assembly bulky, heavy, and inflexible.
Therefore, what is needed is an ultra flexible flex process technology that permits mounting of an increased number of devices in a cost effective weight and space saving manner, transfers heat efficiently away from heat generating devices, and incorporates highly effectual automated roll-to-roll manufacturing concepts.